The invention is aimed at simplifying the task of placing treatment chemicals and other substances into the ground, for the purpose of treating contaminants in groundwater, in-situ. Taking the water out of the ground for treatment is not particularly difficult technically, and if the water is taken out of the ground, the treatment chemicals can be applied to the water, above ground, in a reasonably well controlled manner, in whatever quantities and concentrations are required: but taking large quantities of water out of the ground, treating the water, and putting the treated water back, is very expensive, especially when the contaminant is of the kind that is hazardous in small traces.